Function in college produced noise (6)
I believe the answer is:
cosine
'function' is the definition.
(cosine is a kind of function)
'college produced noise' is the wordplay.
'college' becomes 'c' ().
'produced' indicates an anagram.
'noise' with letters rearranged gives 'osine'.
'c'+'osine'='COSINE'
'in' acts as a link.
(Other definitions for cosine that I've seen before include "Trigonometrical ratio" , "Trig function" , "Ratio in trigonometry" , "Trigonometric function" , "Trig ratio" .)